1. Technical Field
The present invention relates to a lighting device for turning on a discharge lamp, a lighting control device, and a projector.
2. Related Art
A projector which includes a light source, a light modulation device for modulating light emitted from the light source to form an image corresponding to image information, and a projection device for projecting the formed image is known. The light source included in this projector is often constituted by a discharge lamp such as an extra-high pressure mercury lamp containing a discharge space into which a pair of electrodes and discharge substances are sealed. In this case, a lighting control device for controlling lighting of the discharge lamp is equipped. A known type of this lighting control device includes a lighting device for supplying lamp power to the discharge lamp to turn on the discharge lamp, and a control device for controlling the operation of the lighting device (for example, see U.S. Pat. No. 5,463,287).
The lighting control device disclosed in U.S. Pat. No. 5,463,287 includes a converting circuit for controlling output current and output power, an inverter circuit for converting direct current into alternating current, an igniter circuit, a transformer which has a primary coil connected with the igniter circuit and a secondary coil connected with the inverter circuit, and a control circuit (microcomputer) for controlling the respective circuits by using a plurality of drive circuits. According to this lighting control device, the igniter circuit supplies high-voltage ignition pulses to the primary coil of the transformer in response to signals outputted from the control circuit to the drive circuits. As a result, high-voltage pulses generated on the secondary coil of the transformer are applied to the discharge lamp, and discharge is initiated from the discharge lamp.
According to the lighting control device disclosed in U.S. Pat. No. 5,463,287, however, it is possible that high voltage is applied to a control line for connecting the igniter circuit with the control circuit and the drive circuit via the control line. In this case, the control circuit may be damaged. Moreover, noise generated by the high voltage may cause malfunction of the control circuit. Thus, the control circuit needs to be resistant to high voltage and protected from noise, which complicates the structure of the lighting control circuit.